Short term Memory, focus, concentration.

4 months ago i have quit smoking after that i gone through the effects of quitting such as dizziness anxiety depression after that my head started falling back and spinning sensation in head while walking i started googling all these symptoms but right now i am having issues with memory,focus , concentration the thing which happened some time before i am not able to remember strongly, confidence level is very low its like i cant do any task like working out in gym and driving a car first i was not like this but now this all things are happening with me Please suggest some medicines I have donr mri ,xray everything is normal Vitamin d3 Vitamin b12 blood test was low so i am taking that medicines prescribed by doctor